Role of Pasteurella multocida, Pasteurella haemolytica and Salmonella typhimurium porins on inducible nitric oxide release by murine macrophages.

The aim of this study was to verify whether Pasteurella haemolytica, P. multocida and Salmonella typhimurium porins could affect the inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) release by murine resident peritoneal macrophages in vitro. We also compared their effect with that elicited by P. haemolytica, P, multocida and S. typhimurium lipopolysaccharide (LPS) whose biological activity is well known. Variations in NO release and NOS mRNA expression due to variable concentrations of porins were recorded and compared. We also investigated the synergism between bacterial products and interferon gamma (IFN-gamma). With this aim cells were incubated with porins together with murine rIFN-gamma prior to assessing the presence of NO in the supernatant and mRNA analysis. Porins in themselves were not able to induce NO release by resident peritoneal macrophages. Incubation of macrophages with IFN-gamma in the presence of porins increased NO release, whereas incubation in the presence of the arginine analog N-G-monomethyl-L-arginine (NMA) inhibited NO release. The greatest NO release was obtained using porins at a concentration of 5 mu g/mL. Porins, together with IFN-gamma, were also able to upregulate the mRNA expression of iNOS. Our findings suggest that Gram-negative porins are able to modulate inflammatory and immunological responses by affecting the release of NO and the expression of iNOS gene in activated macrophages.